Artifacts are byproducts of digital compression methods such as JPEG and MPEG compression algorithms, which permanently discard some pixels.
The artifacts are especially noticeable in the case where high compression ratios are used thus causing large amounts of pixels to be discarded. As TV screens become larger, the distortions are now more and more noticeable by end users.
Blocking artifacts are a type of artifacts noticeable as abnormally large pixel blocks which are generated when an encoder cannot keep up with the allocated bandwidth. Those blocking artifacts are especially noticeable with fast motion sequences or quick scene changes.
In the case of a digital broadcast configuration, the broadcaster has to pay for a given bandwidth used for delivering a digital video program. On the other end of a transmission link, the end user is looking to receive a video program. The broadcaster may want to optimize the delivery of the digital video program by adjusting the compression algorithm used in order to modify an amount of bandwidth consumed. Such strategy is of great interest for the broadcaster. However the broadcaster may want in such case to be able to react to the appearance of blocking artifacts and reduce temporarily the compression ratio. There is therefore a need for a method for detecting blocking artifacts in an image.
U.S. Pat. No. 6,611,295 discloses an MPEG block detector. More precisely, the patent discloses a method for counting blocking artifacts as a function of their position in a grid. Unfortunately, the results provided may be subjective for the broadcaster since a first blocking artifact may have a larger impact than a second blocking artifact. Counting blocking artifacts therefore suffers from great limitations.
There is a need for a method and apparatus that will overcome at least one of the above-identified drawbacks.
Features of the invention will be apparent from review of the disclosure, drawings and description of the invention below.